Pressure-sensitive copying systems

ABSTRACT

A sheet for use in a pressure-sensitive copying system has a coating of microcapsules containing an organic, initially colourless, colour-former dissolved in a solvent which includes dibenzylbenzenes, specifically a mixture of unsubstituted dibenzylbenzenes with substituted dibenzylbenzenes containing up to three methyl groups.

United States Patent 1 Ross et al.

[4 1 Feb. 11,1975

[ PRESSURE-SENSITIVE COPYING SYSTEMS [75] Inventors: John Edward Ross, Stoke Poges;

David James Marshall, Widmer End, High Wycombe; Brian Samuel Chapman, Prestwood, all of England [73] Assignee: Wiggins Teape Research &

Development Limited, London, England [22] Filed: Sept. 11, 1972 [211 Appl. No.: 287,714

[30] Foreign Application Priority Data Sept. 23, 1971 Great Britain 44474/71 Jan. 20, 1972 Great Britain 2785/72 [52] U.S. Cl. 1l7/36.8, 252/316 [51] Int. Cl 841m 5/16 [58] Field of Search 117/362, 36.8; 252/316;

[56] References Cited UNITED STATES PATENTS 3.0l6,308 l/l962 Macaulay l 17/36.! 3.627.581 l2/l97l Phillips 117/362 FOREIGN PATENTS OR APPLlCATlONS 9l5.342 l/l963 Great Britain 8/94 2,153,634 5/1972 Germany ll7/36.2

Primary ExaminerWilliam D. Martin Assistant Examiner-Bernard D. Pianalto Attorney, Agent, or FirmBurns, Doane, Swecker & Mathis BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to pressure-sensitive copying systems of the kind in which an initially colourless colour-former held in microcapsules is reacted, upon rupturing of the microcapsules by an applied pressure, with a co-reactant material to form distinctive coloured marks. Such systems will be referred to hereinafter as systems of the kind defined above.

Such systems can be of the type in which the microcapsules are carried on one surface of a transfer sheet, referred to as a CB (coated back) sheet and the coreactant material is carried on one surface of a record sheet, referred to as a CF (coated front) sheet, or can be of the autogeneous type in which the microcapsules and the co-reactant material are carried on the same surface ofa single sheet. In systems for providing a plurality of copies, intermediate CFB (coated front and back) sheets are provided.

2. Description of the Prior Art Known CB sheets carry a coating of microcapsules, which may be separate or in capsular units, i.e., clusters of capsules, each microcapsule comprising a wall of hydrophilic colloid material such as gelatin, containing a colourless, chromogenic material (colour-former) of basic reactant chemical properties which in use contacts and is coloured by a co-reactant material, such as attapulgite clay, acid treated montmorillonite clay, or particles of an oil-soluble, acidic phenolic polymeric material (generally in combination with kaolin clay), carried by a CF sheet, to provide distinctive coloured marks on the CF sheet. Such contact and colouration can be caused by rupture of microcapsules by localised pressure from writing, typing or printing on the non-coated front surface ofa CB sheet which is positioned with its coated back surface in contact with the coated front surface of a CF sheet.

Various methods of manufacturing microcapsules and capsular units are well known, as are various methods of coating microcapsules and capsular units on to a base sheet to provide a CB sheet and coating a coreactant material on to a base sheet to provide a CF sheet, and such methods will not therefore be described in detail herein.

Normally the internal phase of a microcapsule, that is the material within the microcapsule wall, comprises one or more. colour-formers which are in the nature of dye substances, typically crystal violet lactone (CVL) and benzoyl leuco methylene blue (BLMB), or 3,3-bis (dialkyl indolyl) phthalides, or 3-dialkylamino- 6-alkyl- 7-alkylamino fluoranes, or 3dialkylamino-7- dialkylamino fluoranes. These colour-formers are dissolved in a solvent, typically hydrogenated terphenyl or mono isopropyl bi-phenyl, and diluted with, for example, kerosene. The dye substances CVL and BLMB are normally used together, since CVL is effective to provide a rapid colouration and BLMBis effective to provide a lasting colouration, on reaction with commonly used co-reactant materials such as those mentioned above.

There are various tests which are used to compare pressure-sensitive copying systems, the two principal tests being the calendar intensity Cl test and the smudge test. Other tests which are used are windowfading, office-fading and ream decline tests. All of these tests are well-known and will not therefore be described in detail herein. It is sufficient to state that the CI test is a measure of print intensity, that is the distinctiveness of the mark produced, and the result is expressed as a percentage, the lower the percentage the better the print intensity, and that the smudge test is a measure of resistance of the CB sheet to accidental rupture of microcapsules, the result being expressed as a number less than 100, the higher the number the better the CB sheets resistance to accidental microcapsule rupture. The window-fading and office-fading tests measure the print intensity after exposure to sunlight and artificial light, respectively, for various periods of time, while the ream decline test measures the initial print intensity obtained with sheets which have been stored in the ream for various periods.

Three other important aspects which are considered when comparing pressure-sensitive copying systems are smell, both during and after manufacture, toxicity and cost.

SUMMARY OF THE INVENTION The present invention is particularly concerned with the internal phase of the microcapsules used in pressure-sensitive copying systems of the kind defined above.

According to the present invention, a sheet for use in a pressure-sensitive copying system comprises a base sheet carrying a coating of the microcapsules, each microcapsule containing an organic, initially colourless,

colour-former dissolved in a solvent which includes dibenzylbenzenes of the general formula:

CH CH R Dibenzylbenzenes: approx. 10 to 15% Methyldibenzylbenzenes: approx. 40%

(including dibenzyltoluene) Dimethyldibenzylbenzenes: approx. 35 to 40% Trimethyldibenzylbenzenes: approx. 10% approx. 99%

the balance consisting ofimpurities of higher molecular weight. Such a mixture is sold in Great Britain under the trade name Lipinol T by Huls (U.K.) Ltd. Lipinol T has a very low level of toxicity in various mammalian species, the lethal dose being in excess of 20 g/kg. Thus, Lipinol T presents no toxic hazard to man under normal conditions when used as the solvent in the internal phase of pressure-sensitive copying system microcapsules.

In comparison with other solvents, the preferred dibenzylbenzenes mixture has the following advantages: cheapness, better initial print intensity (CI test) for a given CB sheet coating weight when used with a CF sheet having an oil-soluble acidic phenolic polymeric material/kaolin clay coating; high colour-former solubility, thus allowing high dilution; slower fade rate with the windowfading test; less smell both during manufacture and from the manufactured CB sheet. Further the preferred mixture has no adverse effects with regard to the officefading and ream decline tests.

The preferred dibenzylbenzenes mixture has a viscosity between 35 and 45 c? at 20C; a density of 1.0 to 1.04 g/ml; a distillation range at 20 mm Hg of 240 to 260C and a flash point of about 180C.

Tests have shown that the preferred dibenzylbenzenes mixtures will dissolve 8.5 w/v CVL and 5.8 w/v BLMB and that it is completely compatible with kerosene which is a standard and preferred diluent.

The preferred dibenzylbenzenes mixture is a suitable solvent for many other colour-formers which are used in pressure-sensitive copying systems, and specifically for:

3,3-bis (dialkyl indolyl) phthalides,

3-dialltylamino-6-alkyl-7-alkylamino fluoranes, and

3-dialkylamino-7-dialkylamino fluoranes.

DETAILED DESCRIPTION OF THE INVENTION Specific embodiments of the invention will now be described on the basis of comparisons between the results of tests on pilot plant produced CB sheets.

EXAMPLE 1 A control CB sheet was produced by coating microcapsules containing a standard internal phase comprising hydrogenated terphenyl as the solvent, kerosene as the diluent, and both CVL and BLMB as colourformers, on to a base sheet with a coating weight of approximately 65 g/m The ratio of solvent to diluent was 4:] w/w.

Similar microcapsules but containing the dibenzylbenzenes mixture sold as Lipinol T as the solvent, and with a solvent to diluent ratio 1:1 w/w, were similarly prepared and were coated on to a base sheet with a coating weight of approximately 6.5 g/m.

The composition of the Lipinol T is given by the suppliers, Huls (U.K.) Ltd as follows:

Compound Quantity (by weight) Dibenzylbenzenes approx. 10 15% Methyldibenzylbenzenes approx. 40% Dimethyldibenzylbenzenes approx. 35 40% Trimethyldibenzylbenzenes approx. l0% Benzyl anthracene and other approx. l%

high condensating materials ACTA CF S/K CF P/K CF Control CB CI 65 Cl 7l CI 75 Invention CB Cl 61 Cl 67 Cl 63 From these results it can be seen that the CB sheet according to the invention gave a better initial print intensity in each case and particularly with P/K CF.

EXAMPLE 2 Similar control and invention CB sheets were prepared but with a coating weight of 6 g/m, and these sheets subjected to window-fading, office-fading and ream decline tests. The results were as follows:

WINDOW-FADING TEST ACTA CF S/K CF P/K CF Control Invention Control Invention Control Invention CB CB CB CB CB CB Initial CI 65 6| 7] 67 75 63 2 days 79 75 71 68 86 83 5 days 84 84 75 75 9| 90 1 week 90 87 79 77 94 93 2 weeks 94 88 84 77 98 97 3 weeks 95 87 86 75 99 98 OFFICE-FADING TEST ACTA CF S/K CF P/K CF Control Invention Control Invention Control Invention CB CB CB CB CB CB Initial Cl 65 61 71 67 75 63 2 days 64 66 62 69 1 week 67 63 68 65 69 64 2 weeks 69 65 69 67 72 7l 3 weeks 66 7I 68 74 REAM DECLINE TEST ACTA CF S/K CF P/K CF Control Invention Control Invention Control lnvention CB CB CB B CB CB Initial Cl 65 6] 71 67 75 63 2 weeks 66 63 71 67 74 62 64 62 71 68 73 62 4 weeks While the specific embodiments of the invention described above all employ the mixture of dibenzylbenzenes sold as Lipinol T, in which the substituents R, to R in the general formula set out above represent hydrogen or up to three methyl groups, it is also possible to use mixtures of said dibenzylbenzenes in which R, to R represent hydrogen, alkyl groups containing less than 5 carbon atoms and alkaryl groups containing 7 or 8 carbon atoms. Preferably, however, R to R represent hydrogen and lower alkyl groups containing less than 3 carbon atoms.

What is claimed is:

l. A sheet for use in a pressure-sensitive copying system, comprising a base sheet carrying a coating of the microcapsules, each microcapsule containing an organic, initially colourless, colour-former, dissolved in a solvent which includes a mixture of dibenzylbenzenes of the general formula where R to R are selected from the group comprising hydrogen, alkyl groups containing less than 5 carbon atoms or alkaryl groups containing 7 or 8 carbon atoms.

2. A sheet according to claim 1 wherein the solvent includes a mixture of said dibenzylbenzenes in which R to R are selected from the group comprising hydrogen or lower alkyl groups containing less than 3 carbon atoms.

Dibenzylbenzenes: approx. 10 to l5% Methyldibenzylbenzenes: approx. 40%

(including dibenzyltoluene) Dimethyldibenzylbenzenes: approx. to

Trimethyldibenzylbenzenes: approx. 10% approx. 99%

the balance consisting of impurities of higher molecular weight.

5. A sheet according to claim 1, wherein the colourformer is selected from the group consisting of:

Crystal violet lactone,

Benzoyl leuco methylene blue,

3,3-bis (dialkyl indolyl) phthalides,

3-dialkylamino-6-alkyl-7-alkylamino fluoranes, and

3-dialkylamino-7-dialkylamino fluoranes.

Disclaimer 3,865,613.J0lm Edward Ross, Stoke Poges, David James MamhaZZ, Widmer End, High Wycombe, and Brian Samuel Chapman, Prestwood, England. PRESSURE-SENSITIVE COPYING SYSTEMS. Patent dated Feb. 11, 1975. Disclaimer filed Apr. 7, 1978, by the assignee, Wiggins Teape Research a Development Limited. Hereby enters this disclaimer to claims 1, 2 and. 5 of said patent.

[Oyfieial Gazette May 30, 1.978.]

Disclaimer 3,865,613.J0lm Edward Ross, Stoke Poges, David James MamhaZZ, Widmer End, High Wycombe, and Brian Samuel Chapman, Prestwood, England. PRESSURE-SENSITIVE COPYING SYSTEMS. Patent dated Feb. 11, 1975. Disclaimer filed Apr. 7, 1978, by the assignee, Wiggins Teape Research a Development Limited. Hereby enters this disclaimer to claims 1, 2 and. 5 of said patent.

[Oyfieial Gazette May 30, 1.978.]

Disclaimer 3,865,613.J0im Edward Ross, Stoke Poges, Dam'd James Marshall, Widmer End, High Wycombe, and Brian Samuel Ohapman, Prestwood, England. PRESSURE-SENSITIVE COPYING SYSTEMS. Patent dated Feb. 11, 1975. Disclaimer filed Apr. 7, 1978, by the assignee, 1 Wiggins Teape Resem'ch oc Development Limited. Hereby enters this disclaimer to claims 1, 2 and 5 of said patent.

[Ofiicz'al Gazette May 30, 1.978.] 

1. A SHEET FOR USE IN A PRESSURE-SENSITIVE COPYING SYSTEM, COMPRISING A BASE SHEET CARRYING A COATING OF THE MICROCAPSULES, EACH MICROCAPSULE CONTAINING AN ORGANIC, INITIALLY COLOURLESS, COLOUR-FORMER, DISSOLVED IN A SOLVENT WHICH INCLUDES A MIXTURE OF DIBENZYLBENZENES OF THE GENERAL FORMULA
 2. A sheet according to claim 1 wherein the solvent includes a mixture of said dibenzylbenzenes in which R1 to R6 are selected from the group comprising hydrogen or lower alkyl groups containing less than 3 carbon atoms.
 3. A sheet according to claim 2 wherein the solvent includes a mixture of said dibenzylbenzenes in which R1 to R6 represent hydrogen and up to three methyl groups.
 4. A sheet according to claim 3 wherein the mixture of dibenzylbenzenes comprises in weight percentages:
 5. A sheet according to claim 1, wherein the colour-former is selected from the group consisting of: Crystal violet lactone, Benzoyl leuco methylene blue, 3,3-bis (dialkyl indolyl) phthalides, 3-dialkylamino-6-alkyl-7-alkylamino fluoranes, and 3-dialkylamino-7-dialkylamino fluoranes. 